Inlet hose diameter

[jjbussell]

Hello,
I have a 2008, 25 with a Cummins/ Mercruiser diesel. (QSD 2.OL) When we run her near the higher end of RPMs the tempature rises quickly, over 210. If I don't back off she will overheat. When I looked at the housing for the impeller I noticed that the inlet is one and a half on the housing but, it goes into a reducer so that the hose is only one inch. Could this be the cause of my problem with the over heating? We changed the impeller last season and cleared out the cooling system.

Thank You,

Ron Bussell

 

[NorthernFocus]

Is your seacock one inch? We have a Cummins equipped 2009 and the inlet hose is 1 1/4 all the way from seacock to pump. Does the strainer run full or can you see air in the top of it? If there is air then the pump is pulling more than can get through the line. If the boat stays in the water the seacock might also be fouled internally with marine growth.

 

[dclagett]

Don’t have a Cummings, however on my Volvo Penta D3 the raw water plumbing is 1 1/4 inch and the thru hull was only 1 inch. I changed the thru hull to 1 1/4 inch along with a wedge scoop (see my album) and that lowered the engine operating temperature about 5 deg F. My engine only overheated at full throttle when a blockage was present. Currently with the change I made in the raw water system full throttle operation maintains an engine temperature around 188 to 190 deg F. From your description of the temperature rising quickly I suspect you have a blockage somewhere in your raw water system.

 

[knotflying]

I believe you should have 1-1/4 inch from the sea cock to the raw water pump. Additionally, if your head is plumbed to the same sea strainer there are instances that you suck in air from the head and hence less water in your system. First check your your coolant level. If you are low, fill it up and make sure you have no leaks. If that all checks out then check that your fittings and everything are 1-1/4. If that checks out then disconnect your head water line and plug it with a wooden plug and see if there is a difference in temperature. After you have done these two tasks. Then check your oil cooler inlet and outlet to make sure there are no weeds blocking flow. You may also see the condition of the cooler that may indicate a flush is needed. You may need to flush your heat exchanger with ridlyme.

 

[BB marine]

I questioned raw water plumbing last winter when I installed my water flow sensor. I have a 1 1/4 raw water hose coming from the strainer to the Volvo Reverse gear cooler. The thru hull fitting is only 1" and the fittings coming off the strainer is 1". 1"nipple,90 degree fitting, nipple and another 90 degree fitting to strainer then 1" pipe thread with a 1 1/4" barb fitting to attach to the required 1 1/4 " system. I believe this to be marginal for the cooling system. It works but any obstruction or fouling in the raw water system could cause cooling issues quicker then a properly sized system. The Water pump used on a D3 has a capacity of 4.9 cuft/min at 18.9 psi @ wot that equals approx 36.5 gallons per minute. A 1" pipe with no restrictions no fittings just straight pipe can flow approx 26 gallons per minute at 20 psi. Figure less flow because of fittings. I have seen a 12 degree increase in temperature from 3000 rpm to 4000 rpm since the first day of owning the boat. This installation works but it is marginal. If the system was all 1 1/4" fittings the gallons per minute goes up to 47 GPM using straight pipe, figure less with fittings but it will meet the capacity of the pump and Volvo's installation specification.

Photo shows 1" fittings

Photo shows 1 1/4" after strainer

 

[captstu]

I had the same problem on my art 25 with Yanmar 150.

It appears the through hole was sized for the old Cummins 110 and never upgraded for the 150.

The folks that have had no problem typically run the engine at low cruise seven knots or so.

If you take it up to 12 nights there just isn’t enough calling.

I had the through hole, the sea chest, and all the tubing changed.

The engine no longer overheats.

The whole project is described on the Boaths website, Shearwater-Sailing.com




Stuart Bell
Ranger 25: Shearwater
(561) 352-1796

 

[NorthernFocus]

We have no problem with the original plumbing. Then again we run in 50 degree water.

 

[captstu]

Nothernfocus: I was thinking of putting ICE in the ICW near Florida - our water gets over 90 degrees in the summer.

BTW, do you run at or near Wide Open Throttle much of the time?

Never thought about the water temperature - clearly must make a difference. I'm guessing that is a contribution to why the factory didn't see the problem. /Stu

 

[BB marine]

We have no problem with the original plumbing. Then again we run in 50 degree water.

This statement is correct. The 50 degree water makes a huge difference in cooling. Our home port is on Lake Michigan. N 42' 44.099
The water temperature in the early season is 50 F and by late summer reaches low 70's. Engine running temperature normally runs 178 F at my high cruise 3350 rpm. WOT 190F. I have in the past never experienced such a temperature differential in boats that I have run unless there was a water restriction in the cooling system. A engine manufacturer sizes the cooling system to maintain an even running temperature and has requirements of supply specifications to maintain proper run-in temperatures so in the event there is a small restriction the engine will still be able to function. When we have cruised on inland rivers with higher water temperatures the engine temperatures ran even warmer 3350rpm 185F to 187F and WOT would climb to 193F to 195F. This was consistent with our trip last year on the Tennessee river. Water Temperatures running average 82F. Along with higher running temperatures of the engine was high air temperatures in the engine compartment. 160F. A boat manufacturer should design a boat to run in the worst case instead of the best case.

As I stated in my previous reply I installed a water flow alarm sensor along with an exhaust over heat temp sensor over the winter. When doing this I noticed the smaller thru hull 1", hose fittings 1" going into the strainer. ( there is a 1 1/4" molded fitting on the strainer but an internal thread was tapped to accept a 1" pipe). Regardless the fitting coming out of the strainer is 1" plus 2 other 3/4" fittings to feed the head and wash down. After I saw this it made sense on why there is such a temperature differential. I looked up the installation specification for the D3 thru hull and seacock. It calls for 1 1/4 thru hull and piping. I looked up in Volvo's parts manual for required thru hull and found part number 1140129 32 MM ID. slightly larger then 1.25 @ 1.259. The smallest Sea strainer that Volvo sells is 32MM. This tells me that while the 1" works it is marginal. Why install marginal equipment?

 

[captstu]

Everything Brian says matches my experience - plus some.

Three issues:

1. Ranger taps the sea strainer to pull off water for the cockpit washdown. This isn't a good idea - my washdown was never used, but it developed an air leak so when the engine ran fast, the raw water pump was sucking air with the water. I removed the sea strainer and plugged the never-should-have-been-there inlet on the strainer and the air leak went away, with some improvement.

2. The cooling system is below Yanmar specs (or it was), so at high RPM and high raw water temp, the engine overheated. Apparently the cooling raw water was sized correctly for the original Cummins 110 engine offered with the original R25s - but as the engine "grew", the cooling system remained the same.

3. The raw water inlet is a sloped screen under the starboard side of the engine. I have posted - elsewhere - the growth inside the strainer since because of the poorly designed elbow in the raw water line, there is no real way to clean or inspect the strainer. I removed the strainer and the elbow and installed a strainer that took water in from the bottom and out from the side - removing the need for the elbow and making it possible to inspect or rod-out the raw water intake (a simple mushroom) should it be necessary.